A team from the Forsyth Institute and the Dana Farber Cancer Institute in Boston found three types of bacteria were present in more than 80% of cases.

The cancer is often diagnosed late usually during dentist examinations followed by testing of tissue samples.

Cancer Research UK said the findings were "exciting" and if confirmed could lead to a screening programme.

Lead researcher Donna Mager said: "Finding bacteria associated with oral cancer encourages us to hope that we have discovered an early diagnostic marker for the disease.

"If future studies bear this out, it may be possible to save lives by conducting large scale screenings using saliva samples."

It raises the prospect of a quick, easy, diagnostic test
Henry Scowcroft, of Cancer Research UK

Researchers said the five-year survival rate for oral cancer is low at 54% because many people are diagnosed late.

They predicted early diagnosis could see as many as 90% survive.

About 4,400 new cases of oral cancer are diagnosed each year in the UK - 1.6% of all new cancers.

The team collected saliva samples from 45 patients with oral squamous cell carcinoma (OSCC), which accounts for 90% of all oral cancers, and 229 without, the Journal Of Translational Medicine reported.

The samples were analysed for 40 different species of bacteria and the team found six were present at much higher levels in the oral cancer patients.

Three of the species - Capnocytophaga gingivalis, Prevotella melaninogenica and Strepococcus mitis - when used to diagnose cancer were found to correctly predict more than 80% of cases.

Bacteria

The team said it could not rule out the possibility that these three bacteria caused the oral cancer, but added more research was needed.

Henry Scowcroft, science information officer at Cancer Research UK, said: "This preliminary work is very exciting. It raises the prospect of a quick, easy, diagnostic test for OSCC, the most common form of oral cancer."

He also said if the findings were confirmed in clinical trials the research could even lead to a screening programme for OSCC.

He added: "This could take place during annual visits to the dentist and may lead to the disease being detected earlier when it is much easier to treat."